PECVD barrier coating systems on post-consumer recyclates for food contact applications

Abstract

As using recyclates in the food sector is currently severely restricted due to the risk of harmful contamination, the reuse of PCR (Post-Consumer Recyclates) could be greatly increased through the development of migration barriers. However, the deposition of functional barrier coatings in PECVD processes (Plasma-Enhanced Chemical Vapour Deposition) on thermoformed PCR polypropylene cups is non-trivial due to complex geometries and difficult surface properties (high roughness, non-polarity, fluctuation of recycylate properties). To develop barriers in this system, material properties of recyclate and virgin material were compared by rheometric and thermal analysis and surface properties of PCR and virgin material cups were analysed morphologically in order to define specific coating challenges. Subsequently, coatings were deposited by PECVD consisting of both, silicon organic intermediate layers (SiOCH) and silicon oxide barrier layers (SiO_x). The barrier, measured by the oxygen transmission rate, could be improved by a factor of about 60 compared to uncoated cups.